1. Field of the Invention
The present invention relates to an ink jet recorder. In particular, the invention relates to an ink jet recorder with an ink supply system including an ink tank and a recording head which are connected by a supply tube.
2. Description of Related Art
A conventional ink jet recorder such as an ink jet printer includes an ink tank and a recording head, which are connected by a supply tube and a return tube. The recorder also includes a pump for circulating ink between the tank and the head.
FIGS. 27-29 of the accompanying drawings schematically show a known ink supply system. With reference to FIG. 27, an ink jet printer 100 includes a sub tank 4a and a head unit, which includes a print head 5a. The tank 4a and the head 5a are connected by two supply tubes 21a and two return tubes 22a. The upstream supply tube 21a is fitted with a circulating pump. The upstream supply tube 21a and the downstream return tube 22a are connected to the downstream supply tube 21a and the upstream return tube 22a, respectively, by a joint 40. The joint 40 has two passages formed through it, one of which communicates with the supply tubes 21a, and the other passage communicates with the return tubes 22a.
Each of the passages is fitted with a filter 32 for removing foreign substances etc. from ink. The head unit is mounted on a carriage, and can reciprocate at high speed over a printing medium. The reciprocating unit is followed by the upstream supply tube 21a and the downstream return tube 22a, which are connected to it. While these tubes 21a and 22a are reciprocating at high speed, waves are generated in the ink in the tubes. If the waves propagate to the head 5a, they affect the characteristics of ink ejection. The filters 32 for the passages also function to prevent the waves from propagating to the head 5a. The filters 32 are positioned horizontally so that ink can flow vertically through them. The ink flowing between the supply tubes 21a moves downward through the associated filter 32. The ink flowing between there turn tubes 22a moves upward through the other filter 32.
Otherwise, the joint 40 and the filters 32 might be positioned in such a manner that ink could flow horizontally through the filters.
Very small air bubbles may be contained in the ink supplied from the sub tank 4a to the recording head 5a. If some of the bubbles are trapped on the filter 32 in the supply line, the trapped bubbles tend to move up buoyantly, and can hardly pass through this filter. Therefore, the trapped bubbles are liable to stay or be retained on the filter 42. The staying bubbles reduces the contact or touch area between the filter 42 and ink, and therefore reduces the effective area of this filter. This prevents a sufficient amount of ink from flowing to the head 5a, and therefore defective recording may occur. The staying bubbles act as dampers, which may hinder or impede the intended normal ink flow when the circulating pump is driven.
As shown in FIGS. 28 and 29, the joint 40 includes a double connector 151, a seal member 152 and a holder 153, which engages with the connector. The double connector 151 includes integral twin connectors, each of which is connected to one of the upstream supply tube 21a and the downstream return tube 22a. Each of the twin connectors is fitted with one of the filters 32 on its bottom. The seal member 152 surrounds bottom portions of the twin connectors. The holder 153 includes integral twin connectors, each of which is connected to one of the downstream supply tube 21a and the upstream return tube 22a. The double connector 151 also includes lock pawls 151a. The holder 153 also includes lock pawls 153a for each engaging with one of the pawls 151a to keep it and the double connector 151 connected. The holder 153 further includes a ridge 153b formed on its top for engaging with the seal member 152 to seal the junctions between the holder 153 and the connector 151. The ridge 153b is positioned away from the passages in the joint 40 and the filters 32. Therefore, gaps are liable to be formed between the ridge 153b and each of the passages and the filters 32. Air bubbles may stay in the gaps. If the bubbles grow larger, they narrow the passages. This makes it impossible to secure the necessary amount of ink flow.
Because the joint 40 includes a number of parts, its production costs are high.
Another conventional ink jet recorder of the foregoing type includes a carriage, on which a head holder can be mounted. The head holder is fitted with a connector. The system also includes an ink tank, which is connected to a supply tube and a return tube. When the head holder is mounted on the carriage, the connector is connected to the tubes. The mounting involves positioning the head holder with high accuracy to align the connector with the tubes.
U.S. Pat. No. 5,359,357, which corresponds to Japanese Patent Application Laid-Open No. 5-318761, discloses an ink jet recorder including a carriage, a head unit, an ink supply tube and an ink return tube. Each of the tubes is connected to a connector. The elasticity of the seal rubber of the connector absorbs the displacement or misalignment of the connector from the associated tube when the head unit is mounted on the carriage. Because the amount of deformation of the seal rubber is limited, however, it is not possible to absorb a large amount of displacement.